"As a gun owner and hunter, I support the Second Amendment rights of Missourians and oppose efforts to undermine them," Nixon says in a statement. "That is why, as Governor, I have enacted legislation to expand gun rights, including bills to strengthen the Castle Doctrine and to allow more Missourians to carry concealed weapons. House Bill 533 is a sensible expansion of Missouri's already strong protections for gun owners."

The general assembly of the state of Missouri strongly promotes responsible gun ownership, including parental supervision of minors in the proper use, storage, and ownership of all firearms, the prompt reporting of stolen firearms, and the proper enforcement of all state gun laws. The general assembly of the state of Missouri hereby condemns any unlawful transfer of firearms and the use of any firearm in any criminal or unlawful activity.

Meanwhile, House Bill 436, the so-called Second Amendment Preservation, is not a responsible expansion of gun rights in Missouri, Nixon says.

The bill would have directly violated the United States Constitution by nullifying federal gun policy and actually criminalizing the enforcement of certain laws. The bill also would have infringed upon the First Amendment, he says.

In addition to the aim of blocking federal gun control, the legislation also sought to curb the publishing of gun owners' names (after a New York newspaper made headlines when it published a database of local handgun permit holders).

"Under well-established legal precedent, state legislation such as House Bill 436 that seeks to resurrect the pre-Civil War concept of nullification would violate the Supremacy Clause," the governor's office says. "The bill also would have made it a crime for anyone to publish the name or other information of someone who owns a firearm."

Nixon says the included broad ban on this kind of speech could lead to bizarre acts of criminality on the part of journalists: "In fact, under this bill, newspaper editors around the state that annually publish photos of proud young Missourians who harvest their first turkey or deer could be charged with a crime."

The governor's press announcement includes a long list of Nixon's record on gun rights, noting that he signed legislation lowering the right-to-carry age for active duty military in Missouri. He also signed into law a "Castle Doctrine" bill that allows small business owners and farmers to use deadly force on intruders on property they own or lease.

In case there was any doubt, the governor's office even outlines his work as attorney general related to gun rights:

In 2008, then-Attorney General Nixon was among the first attorneys general in the nation to file a brief with the U.S. Supreme Court urging it to strike down the Washington, DC gun ban and adopt the position that the Second Amendment guarantees an individual right to keep and bear arms. He also defended Missouri's conceal carry law before the Missouri Supreme Court and obtained reciprocity agreements from other states to recognize Missouri's conceal carry permits, making Missouri's endorsement the most widely recognized in the nation.

Here's a copy of House Bill 533 and House Bill 436, along with Nixon's full veto statement.